Ball screw



FIG. 1 is a front perspective view of a ball screw;

FIG. 2 is a back perspective view of thereof;

FIG. 3 is a front view thereof;

FIG. 4 is a back view thereof;

FIG. 5 is a left side view thereof, a right side view being a mirror image of the left side view;

FIG. 6 is a top view thereof;

FIG. 7 is an enlarged view of portion 7-7 of FIG. 3;

FIG. 8 is an enlarged view of portion 8-8 of FIG. 4; and,

FIG. 9 is an enlarged view of portion 9-9 of FIG. 4.

The broken lines represent environment and form no part of the claimed design. 

CLAIM The ornamental design for a ball screw, as shown and described. 